Modern spark ignition internal combustion engines typically benefit high initial ignition discharge energy to initiate combustion. It is also known that a long duration spark discharge enhances combustion repeatability if, for example, poor distribution of the air-fuel mixture occurs. However, extended operation at unnecessarily high discharge currents may cause undesirable spark plug electrode erosion. It has been suggested to use two ignition coils isolated with high voltage diodes to combine the two coil outputs to provide the desired high initial discharge current and lower extended discharge current to a spark-plug. However, such a dual coil system undesirably increases the cost of an ignition system.